Hemes labelled in selected positions with deuterium, tritium, or carbon-13 will be synthesized for use as NMR probes into structure-function relationships in heme proteins such as myoglobin, hemoglobin, and cytochromes. The synthetic compounds will be reconstituted into myoglobins and hemoglobins, or biosynthesized into cytochromes, and will facilitate assignments of heme-associated resonances in these proteins by difference spectroscopy for protons, and directly in the deuterium, tritium, and carbon-13 spectra. Two fundamental approaches will be followed for synthesis of labelled hemes: Carbon-13 and some deuterium labelled derivatives of protoporphyrin-IX will be prepared by total synthesis using our newly developed and highly efficient route through tripyrrenes and a,c-biladienes. The a,c-biladienes will be cyclized to porphyrins using the cupric salt method, and time will be spent on a mechanistic study of this intriguing reaction. A mono-meso deuterated derivative of protoporphyrin-IX will be synthesized so as to test the validity of NMR model for heme catabolism to bilirubin. The second approach to labelled hemes will utilize deuterium (or tritium) exchange of protoporphyrin-IX and some derivatives when this is feasible. In particular, a new facet of porphyrin chemistry discovered by the P.I. will be exploited to incorporate hydrogen labels regioselectively into the ring methyls of phorphyrins, as well as the more obvious sites adjacent to activating carbonyl functions. Time will also be spent in characterization of the range of application and structural dependence of the novel exchange reaction and in a study of the effect of metal to porphyrin interactions on a novel electrophilic exchange process.